An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A general tendency, course, or direction.

From M.E. trenden "to roll about, turn, revolve," from O.E. trendan, (cf. O.E. trinde "round lump, ball," O.Fris. trind, M.L.G. trint "round," M.L.G. trent "ring, boundary," Du. trent "circumference," Dan. trind "round").

Ravâl, from row present stem of raftan "to go, walk, proceed" (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack") + suffix -âl, → -al.